Not south of San Antonio, but I carp fish in Austin. Lake Austin is absolutely overrun with grass carp, to the point that the city wants them gone because they are eating all of the vegetation out of the lake. And Lady Bird Lake, in the southernmost part of Austin, is known for having some big commons, and I’ve personally seen people pull some big ones out. And Lake Decker, also in Austin, is known to be a great spot for smallmouth buffalo (I know that buffs aren’t carp, but they’re also really fun to catch so I thought I’d throw that in). As far as I’ve heard, Austin is probably the best spot for carp in Texas. I just got my hands on some method leads and I’m gonna be heading to Austin to try them out on Lady Bird Lake soon.